The present invention relates to a method for backward-signaling of a transmission service which is to be used for a call which is to be set up from a telecommunication network, where the call enters a mobile radio network. When a telecommunication terminal sets up a call to another telecommunication terminal, with the called telecommunication terminal being in the service area of a mobile radio network and the calling telecommunication terminal being in the service area of another telecommunication network, it is generally possible that a transmission service which the calling telecommunication terminal requires cannot be clearly identified in the mobile radio network of the called telecommunication terminal. Accordingly, the selection of a specific transmission service is down to the called telecommunication terminal or the relevant subscriber. On the basis of the related art, the transmission service selected by the called telecommunication terminal is not transmitted to all network nodes which are involved in a call which is to be set up or in a data transmission which can be performed. In a mobile radio network, this particularly means that the access mobile switching centers involved in a call which is to be set up, such as a “Gateway MSC” (Mobile Switching Center) or a “Gateway MSC Server”, which act as connecting network nodes between the mobile radio network and other telecommunication networks, receive no information about the transmission service which is actually to be used for a call entering the mobile radio network, that is to say an “MTC” (Mobile Terminated Call). Accordingly, the access mobile switching centers, such as the “Gateway MSC” and the “Gateway MSC Server”, cannot execute any transmission-service-specific functions. Examples of such transmission-service-specific functions are blocking of particular transmission services, either generally or just for selected connected telecommunication networks, or provision of information about the selected transmission service at this access mobile switching center or at this connecting network node, such as billing information for subscriber or intermediate-network billing.
To date, the calling telecommunication terminal specifies a transmission service it requires by setting particular values in a “Bearer Capability” information element (BC). In addition, bearer services can be described using a “Low Layer Compatibility” information element (LLC) and teleservices can be described using a “High Layer Compatibility” information element (HLC). While LLC and HLC are transmitted unchanged between the telecommunication terminals by transmission networks involved in the transmission or in the call which is to be set up, the BC is valid only in the respective transmission network and is converted, if appropriate, at the network boundary between the transmission networks in question. For this reason, a distinction is also drawn between a PLMN-BC for the mobile radio network and an ISDN-BC for an ISDN landline network as a further telecommunication network. Mobile-radio-specific parameters, including message types, for example, are specified in 3GPP TS 24.008 and 3GPP TS 48.008. ISDN-related parameters and values and also message types can be found in ITU-T Q.760-769 and ITU-T Q.931.
In the case of a call from a landline network to a mobile radio network, as is to be considered here, these parameters are to date transmitted in an “IAM” message (Initial Address Message) when the call is set up, as defined for the “ISUP” in ITU-T Q.760-769. Generally, these parameters are not complete or are missing entirely. However, one cause of this may be that the calling telecommunication terminal provides information about the parameters only incompletely, for example. The quantity of parameters required for describing a transmission service is defined in different ways for different networks. Whereas the GSM standard in a mobile radio network is very restrictive and requires a multiplicity of parameters (3GPP TS 27.001), there are no specific stipulations in an ISDN network using the “ISUP” control mechanism. In addition, there are also different products which set the parameters in different ways. It is also conceivable for a transmission network which is likewise involved in the call setup to transmit the information regarding the parameters possibly only in part or not all. Furthermore, it is possible that the call comes from an analog landline network (PSTN). In this case, the transmission service is not signaled when a call is set up. In analog networks, a call is set up and then the transmission service is flagged at the start of the transmission. To this end, the telecommunication terminals interchange signal tones such as can be heard for a fax transmission, for example. When changing from an analog to a digital telecommunication network, a BC is then often produced which then contains only the information “3.1 kHz Audio”, for example. The BC is therefore incomplete.
A mobile radio network, such as a GSM or UMTS network, for example, in which a call is incoming is already aware of various methods for identifying a transmission service required by a calling telecommunication terminal. First, there is a “multi-numbering method” for this. This involves the transmission service being identified by an appropriate call number, since in this case each transmission service which the telecommunication terminal or the relevant subscriber is authorized to use is assigned its own call number in the mobile radio network. A “Home Location Register (HLR)” in the mobile radio network manages the call numbers associated with the respective transmission services and stores PLMN-BCs belonging to these. The PLMN-BC belonging to the call number associated with a particular transmission service is transmitted to the called telecommunication terminal. That is to say that the PLMN-BC associated with the identified transmission service is communicated to the called telecommunication terminal via a destination mobile switching center, known as a “Visited MSC”, or via a “Visited MSC Server”. The access mobile switching centers through which it passes, namely a “Gateway MSC” or a “Gateway MSC Server”, can in this case optionally be informed about the respective transmission service. In this context, they are supplied with a code which is specific to the respective transmission service. This practice is described in 3GPP TS 29.002, for example. However, this code does not describe the relevant transmission service sufficiently accurately to be able to provide transmission-service-specific functions on the “Gateway MSC” or the “Gateway MSC Server”. The code is therefore too inaccurate, since it makes no statements about a resource allocation in the mobile radio network as requested by the call which is to be set up. In addition, various transmission services need to be distinguished which bear the same code. Examples which may be mentioned in this context are a general synchronous transmission service and a synchronous transmission service for multimedia—both bear the code for BS30, as defined in 3GPP TS 22.002 and 3GPP TS 29.002.
In addition, there is a “single-numbering method”, which attempts to map a PLMN-BC from an ISDN-BC. This procedure is not always successful, however, for example because the ISDN-BC is incomplete or too inaccurate. The called telecommunication terminal then receives no information about the required transmission service, with the exception of a possible incomplete backup BC, as explained in 3GPP TS 24.008 and 3GPP TS 29.007. The transmission service to be used for the call which is to be set up is then ultimately selected by the called telecommunication terminal.
In both methods described, however, the situation is that parameters which define the transmission service to be used are negotiated between the “Visited MSC” or the “Visited MSC Server” and the called telecommunication terminal. This is described in 3GPP TS 27.001 and 3GPP TS 29.007. Following receipt of the “assignment complete” message, the “Visited MSC” or the “Visited MSC Server” contains the information about the transmission service which is to be used. Hence, on the basis of the related art, the complete information about the transmission service to be used is available only in the “Visited MSC” or the “Visited MSC Server” following receipt of the “call complete” message from the called telecommunication terminal and following receipt of the “assignment complete” message from the “BSS” (Base Station System).
In addition, at the TSG CN-#-21 standardization meeting from Sep. 17.-Sep. 19, 2003, a document NP-030431 about “internetwork accounting for BS30-based services such as video” presented a solution which can be used to provide billing information to a network boundary between a mobile radio network and a landline network. This solution makes use of apparently unused bits of an “Optional Backward Call Indication” parameter contained in the “Address Complete Message (ACM)” or “Answer Message (ANM)” ISUP messages. This solution can be used only conditionally, however, since the 4 free bits of the “Optional Backward Call Indication” parameter are insufficient to be able to provide all requested transmission-service-specific functions on a “Gateway MSC” or a “Gateway MSC Server”. In addition, these bits are already used in some national applications and are therefore not available without restriction.